if you go on the centrelink website (Centrelink Home Page) go to the 'online services' heading, on that page there is a Rate Estimator you can enter in info about your current or proposed circumstances and it will calculate an estimate of your possible entitlements. You dont need to log in to use it, and it doesnt save your info . You'll be able to get the family tax benefit, and when you return to work for the first time after you get an exempt period which will give you more money.
Based on your DF's salary with you not working you'd probably get about $300 per fornight if that, and prob could get anothr $15pf from parenting payment partnered.. but do the estimate thing (its the same ting c'links people use when you ask them for an estimate)

And maybe do a little rebudgeting,
It can be done, ive got baby #3 on the way and DP's income is less than $40,000 - ive done alot of re-budgeting/financing and we're getting by so dont stress too much! we dont want you going into early labour from stress